This invention relates to an antivibration elastic support with an incorporated damping device, applicable particularly to the suspension of the power plants of automobiles.
It is known that these elastic supports have the main role of filtering vibrations due to imperfections in the balance of the engine. For this reason, these supports should have a great flexibility. Unfortunately, this leads to a considerable deterioration of comfort under the effect of low-frequency vibrations coming from the road; these latter vibrations are transmitted because of insufficient damping of the supports which are generally made of elastomer. In other words, the desired characteristics are:
a well defined static rigidity, because the prime role of such a support is to carry the static load that is applied to it;
a certain damping, during stresses of low frequency up to 10 to 20 Hertz and of great amplitude on the order of 0.5 to 5 mm to limit the vibrations of the suspended mass;
a slight dynamic stiffening at high frequencies of about 50 to 300 Hertz to preserve good characteristics of filtering these vibrations which are generators of noise.
One of the properties of viscoelastic materials of the elastomer type is the increase of the rate of dynamic stiffening with the frequency, therefore the progressive degradation of filtering of the vibrations. This increase is the more pronounced the more the mixture is damping. Advances made in formulating the mixtures often end in acceptable compromises. However, it appears that the limit of the possibilities of improvement by this means has now been reached.
Devices are already known which make it possible to separate the "damping" function from the "rigidity" function. One of them associates a flexible elastic support with a shock absorber, but this solution is costly and inefficient for damping oscillations of slight amplitude, because of mechanical frictions in the shock absorbers. Further, installation of shock absorbers can be particularly difficult in the small volume of an engine compartment.
Other solutions consist in incorporating a hydraulic or pneumatic damping device in the support itself by using the deformation of the support itself to displace a fluid through an orifice. These solutions are not perfectly satisfactory because they do not give sufficient consideration to the existence of different amplitude vibrations. Further, these devices generally exhibit large dimensions, result in a gain in damping overall only in a single direction of stress and do not make it possible to obtain a given rate of rigidities in two perpendicular directions which is generally desired by automobile manufacturers.